The present invention relates to an optical pickup device for conducting recording and/or reproducing for an optical information recording medium and to an objective lens used in the optical pickup device.
In an optical system of an optical pickup device wherein DVD (digital versatile disk) representing an optical disk (optical information recording medium) is used as a medium, there is used a laser having a wavelength of about 650 nm (for example, see Patent Document 1).
In recent years, there has been advanced development of HD-DVD (high density DVD) representing an optical disk that is similar to DVD in terms of a size and is greater than DVD in terms of capacity. In the optical system of the optical pickup device employing this HD-DVD as a medium, a diameter of the light-converging spot is made small by using a violet laser with a short wavelength (380–450 nm approximately), for the purpose of achieving high density of recording signals or of reproducing high density recording signals.
(Patent Document)
                1. TOKKAIHEI No. 11-337818        2. TOKKAIHEI No. 6-242373        